[PATCH 00/12, v2] x86/mm: Implement lockless pgd_alloc()/pgd_free()
From: Ingo Molnar
Date: Sat Jun 13 2015 - 05:49:50 EST
The purpose of this series is:
Waiman Long reported 'pgd_lock' contention on high CPU count systems and proposed
moving pgd_lock on a separate cacheline to eliminate false sharing and to reduce
some of the lock bouncing overhead.
I think we can do much better: this series eliminates the pgd_list and makes
pgd_alloc()/pgd_free() lockless.
This is the -v2 submission that addresses all feedback received so far, it
fixes bugs and cleans up details. There's a v1->v2 interdiff attached
further below: most of the changes relate to locking the task before looking
at tsk->mm.
The series is also available in -tip:master for easy testing:
git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master
It's not applied to any visible topic tree yet. (Its sha1 is bc40a788fc63
if you want to test it without pending non-x86 bits in -tip.)
Thanks,
Ingo
====================>
Ingo Molnar (12):
x86/mm/pat: Don't free PGD entries on memory unmap
x86/mm/hotplug: Remove pgd_list use from the memory hotplug code
x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()
x86/mm/hotplug: Simplify sync_global_pgds()
mm: Introduce arch_pgd_init_late()
x86/mm: Enable and use the arch_pgd_init_late() method
x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code
x86/mm: Remove pgd_list use from vmalloc_sync_all()
x86/mm/pat/32: Remove pgd_list use from the PAT code
x86/mm: Make pgd_alloc()/pgd_free() lockless
x86/mm: Remove pgd_list leftovers
x86/mm: Simplify pgd_alloc()
arch/Kconfig | 9 ++++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/pgtable.h | 3 --
arch/x86/include/asm/pgtable_64.h | 3 +-
arch/x86/mm/fault.c | 31 +++++++++-----
arch/x86/mm/init_64.c | 80 ++++++++++++-----------------------
arch/x86/mm/pageattr.c | 41 +++++++++---------
arch/x86/mm/pgtable.c | 131 ++++++++++++++++++++++++++++++----------------------------
arch/x86/xen/mmu.c | 51 +++++++++++++++++------
fs/exec.c | 3 ++
include/linux/mm.h | 6 +++
kernel/fork.c | 16 +++++++
12 files changed, 209 insertions(+), 166 deletions(-)
-v1 => -v2 interdiff:
====
arch/x86/mm/fault.c | 17 +++++++++++------
arch/x86/mm/init_64.c | 23 ++++++++++++-----------
arch/x86/mm/pageattr.c | 27 ++++++++++++++-------------
arch/x86/mm/pgtable.c | 22 ++++++++++++----------
arch/x86/xen/mmu.c | 47 +++++++++++++++++++++++++----------------------
fs/exec.c | 2 +-
include/linux/mm.h | 4 ++--
kernel/fork.c | 4 ++--
8 files changed, 79 insertions(+), 67 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index bebdd97f888b..14b39c3511fd 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -237,28 +237,33 @@ void vmalloc_sync_all(void)
struct task_struct *g, *p;
- rcu_read_lock();
- spin_lock(&pgd_lock);
+ spin_lock(&pgd_lock); /* Implies rcu_read_lock(): */
for_each_process_thread(g, p) {
+ struct mm_struct *mm;
spinlock_t *pgt_lock;
pmd_t *pmd_ret;
- if (!p->mm)
+ task_lock(p);
+ mm = p->mm;
+ if (!mm) {
+ task_unlock(p);
continue;
+ }
/* The pgt_lock is only used on Xen: */
- pgt_lock = &p->mm->page_table_lock;
+ pgt_lock = &mm->page_table_lock;
spin_lock(pgt_lock);
- pmd_ret = vmalloc_sync_one(p->mm->pgd, address);
+ pmd_ret = vmalloc_sync_one(mm->pgd, address);
spin_unlock(pgt_lock);
+ task_unlock(p);
+
if (!pmd_ret)
break;
}
spin_unlock(&pgd_lock);
- rcu_read_unlock();
}
}
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 730560c4873e..dcb2f45caf0e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -171,28 +171,28 @@ void sync_global_pgds(unsigned long start, unsigned long end)
const pgd_t *pgd_ref = pgd_offset_k(address);
struct task_struct *g, *p;
- /*
- * When this function is called after memory hot remove,
- * pgd_none() already returns true, but only the reference
- * kernel PGD has been cleared, not the process PGDs.
- *
- * So clear the affected entries in every process PGD as well:
- */
+ /* Only sync (potentially) newly added PGD entries: */
if (pgd_none(*pgd_ref))
continue;
- spin_lock(&pgd_lock);
+ spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
for_each_process_thread(g, p) {
+ struct mm_struct *mm;
pgd_t *pgd;
spinlock_t *pgt_lock;
- if (!p->mm)
+ task_lock(p);
+ mm = p->mm;
+ if (!mm) {
+ task_unlock(p);
continue;
- pgd = p->mm->pgd;
+ }
+
+ pgd = mm->pgd;
/* The pgt_lock is only used by Xen: */
- pgt_lock = &p->mm->page_table_lock;
+ pgt_lock = &mm->page_table_lock;
spin_lock(pgt_lock);
if (!pgd_none(*pgd_ref) && !pgd_none(*pgd))
@@ -202,6 +202,7 @@ void sync_global_pgds(unsigned long start, unsigned long end)
set_pgd(pgd, *pgd_ref);
spin_unlock(pgt_lock);
+ task_unlock(p);
}
spin_unlock(&pgd_lock);
}
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 93c134fdb398..4ff6a1808f1d 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -440,29 +440,30 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
if (!SHARED_KERNEL_PMD) {
struct task_struct *g, *p;
- rcu_read_lock();
+ /* We are holding pgd_lock, which implies rcu_read_lock(): */
for_each_process_thread(g, p) {
+ struct mm_struct *mm;
spinlock_t *pgt_lock;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
- if (!p->mm)
- continue;
+ task_lock(p);
+ mm = p->mm;
+ if (mm) {
+ pgt_lock = &mm->page_table_lock;
+ spin_lock(pgt_lock);
- pgt_lock = &p->mm->page_table_lock;
- spin_lock(pgt_lock);
+ pgd = mm->pgd + pgd_index(address);
+ pud = pud_offset(pgd, address);
+ pmd = pmd_offset(pud, address);
+ set_pte_atomic((pte_t *)pmd, pte);
- pgd = p->mm->pgd + pgd_index(address);
- pud = pud_offset(pgd, address);
- pmd = pmd_offset(pud, address);
- set_pte_atomic((pte_t *)pmd, pte);
-
- spin_unlock(pgt_lock);
+ spin_unlock(pgt_lock);
+ }
+ task_unlock(p);
}
-
- rcu_read_unlock();
}
#endif
}
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index b1bd35f452ef..d7d341e57e33 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -348,15 +348,17 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
* at the highest, PGD level. Thus any other task extending it
* will first update the reference PGD, then modify the task PGDs.
*/
-void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd)
+void arch_pgd_init_late(struct mm_struct *mm)
{
/*
- * This is called after a new MM has been made visible
- * in fork() or exec().
+ * This function is called after a new MM has been made visible
+ * in fork() or exec() via:
+ *
+ * tsk->mm = mm;
*
* This barrier makes sure the MM is visible to new RCU
- * walkers before we initialize it, so that we don't miss
- * updates:
+ * walkers before we initialize the pagetables below, so that
+ * we don't miss updates:
*/
smp_wmb();
@@ -365,12 +367,12 @@ void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd)
* ptes in non-PAE, or shared PMD in PAE), then just copy the
* references from swapper_pg_dir:
*/
- if (CONFIG_PGTABLE_LEVELS == 2 ||
+ if ( CONFIG_PGTABLE_LEVELS == 2 ||
(CONFIG_PGTABLE_LEVELS == 3 && SHARED_KERNEL_PMD) ||
- CONFIG_PGTABLE_LEVELS == 4) {
+ CONFIG_PGTABLE_LEVELS == 4) {
pgd_t *pgd_src = swapper_pg_dir + KERNEL_PGD_BOUNDARY;
- pgd_t *pgd_dst = pgd + KERNEL_PGD_BOUNDARY;
+ pgd_t *pgd_dst = mm->pgd + KERNEL_PGD_BOUNDARY;
int i;
for (i = 0; i < KERNEL_PGD_PTRS; i++, pgd_src++, pgd_dst++) {
@@ -387,8 +389,8 @@ void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd)
* it won't change from under us. Parallel updates (new
* allocations) will modify our (already visible) PGD:
*/
- if (pgd_val(*pgd_src))
- WRITE_ONCE(*pgd_dst, *pgd_src);
+ if (!pgd_none(*pgd_src))
+ set_pgd(pgd_dst, *pgd_src);
}
}
}
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 87a8354435f8..70a3df5b0b54 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -855,27 +855,28 @@ void xen_mm_pin_all(void)
{
struct task_struct *g, *p;
- rcu_read_lock();
- spin_lock(&pgd_lock);
+ spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
for_each_process_thread(g, p) {
+ struct mm_struct *mm;
struct page *page;
pgd_t *pgd;
- if (!p->mm)
- continue;
-
- pgd = p->mm->pgd;
- page = virt_to_page(pgd);
+ task_lock(p);
+ mm = p->mm;
+ if (mm) {
+ pgd = mm->pgd;
+ page = virt_to_page(pgd);
- if (!PagePinned(page)) {
- __xen_pgd_pin(&init_mm, pgd);
- SetPageSavePinned(page);
+ if (!PagePinned(page)) {
+ __xen_pgd_pin(&init_mm, pgd);
+ SetPageSavePinned(page);
+ }
}
+ task_unlock(p);
}
spin_unlock(&pgd_lock);
- rcu_read_unlock();
}
/*
@@ -980,24 +981,26 @@ void xen_mm_unpin_all(void)
{
struct task_struct *g, *p;
- rcu_read_lock();
- spin_lock(&pgd_lock);
+ spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
for_each_process_thread(g, p) {
+ struct mm_struct *mm;
struct page *page;
pgd_t *pgd;
- if (!p->mm)
- continue;
-
- pgd = p->mm->pgd;
- page = virt_to_page(pgd);
+ task_lock(p);
+ mm = p->mm;
+ if (mm) {
+ pgd = mm->pgd;
+ page = virt_to_page(pgd);
- if (PageSavePinned(page)) {
- BUG_ON(!PagePinned(page));
- __xen_pgd_unpin(&init_mm, pgd);
- ClearPageSavePinned(page);
+ if (PageSavePinned(page)) {
+ BUG_ON(!PagePinned(page));
+ __xen_pgd_unpin(&init_mm, pgd);
+ ClearPageSavePinned(page);
+ }
}
+ task_unlock(p);
}
spin_unlock(&pgd_lock);
diff --git a/fs/exec.c b/fs/exec.c
index c1d213c64fda..4ce1383d5bba 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -862,7 +862,7 @@ static int exec_mmap(struct mm_struct *mm)
active_mm = tsk->active_mm;
tsk->mm = mm;
- arch_pgd_init_late(mm, mm->pgd);
+ arch_pgd_init_late(mm);
tsk->active_mm = mm;
activate_mm(active_mm, mm);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 35d887d2b038..a3edc839e431 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1135,9 +1135,9 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
void *buf, int len, int write);
#ifdef CONFIG_ARCH_HAS_PGD_INIT_LATE
-void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd);
+void arch_pgd_init_late(struct mm_struct *mm);
#else
-static inline void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd) { }
+static inline void arch_pgd_init_late(struct mm_struct *mm) { }
#endif
static inline void unmap_shared_mapping_range(struct address_space *mapping,
diff --git a/kernel/fork.c b/kernel/fork.c
index 1f83ceca6c6c..cfa84971fb52 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1605,8 +1605,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
* NOTE: any user-space parts of the PGD are already initialized
* and must not be clobbered.
*/
- if (p->mm != current->mm)
- arch_pgd_init_late(p->mm, p->mm->pgd);
+ if (!(clone_flags & CLONE_VM))
+ arch_pgd_init_late(p->mm);
proc_fork_connector(p);
cgroup_post_fork(p);
--
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